Many reservoirs containing vast quantities of oil have been discovered in subterranean formations; however, the recovery of oil from subterranean formations has been very difficult due to the relatively high viscosity of the oil and/or the presence of viscous tar sands in the formations. In particular, when a production well is drilled into a subterranean formation to recover oil residing therein, often little or no oil flows into the production well even if a natural or artificially induced pressure differential exits between the formation and the well. To overcome this problem, various thermal recovery techniques have been used to decrease the viscosity of the oil and/or the tar sands, thereby making the recovery of the oil easier.
One such thermal recovery technique utilizes steam to thermally stimulate viscous oil production by injecting steam into a wellbore to heat an adjacent subterranean formation. However, the steam typically is not evenly distributed throughout the wellbore, resulting in a temperature gradient along the wellbore. As such, areas that are hotter and colder than other areas of the wellbore, i.e., hot spots and cold spots, undesirably form in the wellbore. The cold spots lead to the formation of pockets of oil that remain immobile. Further, the hot spots allow the steam to break through the formation and pass directly to the production well, creating a path of least resistance for the flow of steam to the production well. Consequently, the steam bypasses a large portion of the oil residing in the formation, and thus fails to heat and mobilize the oil. A need therefore exists to more evenly distribute the steam throughout the wellbore during its injection and to restrict the recovery of the steam, thereby reducing the amount of hot spots and cold spots in the wellbore.